The present invention relates to obstacle monitoring pipeline pigs used in checking the interior of a pipeline for obstacles which might impede the movement of subsequently used pipeline inspecting devices or which exceed industry guidelines.
A number of caliper pigs are on the market that provide detection of anomalies inside pipelines. They are usually expensive to produce and operate. These existing pigs monitor all restrictions along a pipeline regardless of the size of the anomalies. They normally collect a significant amount of data that requires interpretation by a technician or computer programs. This type of caliper pigs is represented, for instance, by the disclosure of U.S. Pat. Nos. 4,953,412 and 5,088,336 (both Rosenberg et al.) and also by U.S. Pat. No. 3,755,908 (VerNooy). The disclosures of the above patents are incorporated herein by reference.
U.S. Pat. No. 4,481,816 (Prentice) describes a caliper pig provided with a monitoring arrangement comprising a substantially circular array of detecting, portions which deform upon contact with the interior surface of the pipeline and remain deformed to provide an indication that the minimum radial distance has been exceeded. Viewed from the standpoint of the present invention, the device disclosed is of a relatively complex structure and allows only a single use of the detecting portions. Also, if a relatively large deformity is encountered prior to reaching a somewhat smaller deformity, the latter may be undetected.
U.S. Pat. No. 4,227,309 (Jones) describes a pipeline pig which includes a flexible disc at a foremost part of the body. The disc is fixedly secured to the body of the pig and is provided with strain gauges which transmit deformations of the disc to electrical impulses to show which portion of the disc has been deformed by an abnormality within the pipeline. The use of the strain gauges renders the overall structure of the flexible disc complex thus increasing the cost of replacement of a damaged disc. Furthermore, the strain gauges are too sensible for the rough working environment of a damaged pipeline and may therefore produce false readings. The piezo electric strip was found working as a microphone; it recorded all vibrations and one could not differentiate between the vibrations and restrictions. Vibrations of the body and thus of the disc are often encountered in use of the pig. There is no backup system which would indicate, at least roughly, the location of an abnormality in case of failure of the electronic system. The location of the disc at the foremost end of the body is disadvantageous as distorted readings of the deformation of the disc by an abnormality occur at a straight portion of the pipeline and in bends of the pipeline. Also, the disc being fixedly secured to the body, it cannot maintain the same angular clock position as it inevitably changes such position with the rotation of the pig about its longitudinal axis. Such rotation may occur when an abnormality is encountered by the guiding cups. The device therefore is not capable of showing the clock position of an abnormality instantly recorded.
U.S. Pat. No. 4,299,033 (Kiley et al.) presents a calipering tool for oil wells or the like applications. It operates with a plurality of feelers which are in a constant contact with the pipe of a well. The tool is of a complex structure. While it may be useful in calipering wells, it is not suitable for applications where only major deformities of the pipe are required to be discovered to avoid damage to a subsequently used caliper pig. Also, the tool of this reference is raised and lowered by means of a suspension cable which cannot be used in pipeline calipers as they often have to travel long distances of tens of miles.
U.S. Pat. No. 4,443,948 (Reeves) describes a pig for monitoring the internal surface profile of a pipeline. It is provided with a plurality of sensors which are in constant contact with the inner surface of the monitored pipeline. A complex system is required to compare output signals from the sensors with an expected value and reference signal generated when they differ by more than a predetermined amount.
U.S. Pat. No. 4,457,073 (Payne) shows a pipeline pig with sensing means capable of monitoring small changes in the internal configuration of a pipeline. A complex mechanism is used to monitor dragging effect to which an elastomeric cap is submitted upon encountering an obstacle. A major obstacle would most likely destroy or at least damage the mechanism used to record the deformities, as the radial cup is in a constant contact with the interior of the monitored pipeline.
U.S. Pat. No. 4,098,126 (Howard) is provided with a plurality of sensors disposed about the circumference of a resilient holding cup. A spring system forces the sensors against the inside of the pipeline. The device is suitable for monitoring relatively small deformities but would become damaged if a major or sharp deformity is encountered. It is of relatively complex structure with a number of flat spring elements constantly pressing the sensors against the pipeline.
U.S. Pat. No. 4,091,678 (Potter) shows a device for detecting dents or out of round conditions of a buried pipeline. The pig contains two concentric rings. The outer ring is sized to accurately fit the inspected pipeline. It carries on its inner surface electrical contacts adapted to co-operate with contacts provided on the outer surface of the inner ring to close an electric circuit when the outer ring is deformed radially inwardly. The device may be suitable for detecting minor anomalies of the cross-section of the pipeline. Larger deformities would destroy or at least damage the system of coaxial rings.
It is an object of the present invention to provide an obstacle monitoring or caliper pig which would be of a simple structure permitting relatively low manufacturing costs, monitoring only major obstacles of a predetermined minimum magnitude and providing a simple operation.
In general terms the invention provides a caliper pig for detecting an obstruction in a pipeline, having an elongated body including a front end and a rear end and comprising carrying guide rings at said front and rear ends for supporting the body in a coaxial sliding engagement with the interior of the pipeline and driving the body through the pipeline, the front end first, using the flow of fluid in the pipeline, said body further carrying a coaxial, generally disc-shaped, detector operatively associated with transfer mechanism including a converting member movable relative to the body responsive to a generally axial force to transmit a mechanical impulse developed at the detector to activate and to deactivate an electrical signal producing device housed in said body, wherein
(I) said detector has an outer diameter smaller than the inside diameter of the pipeline to define therewith a generally annular void having a predetermined radial clearance;
(ii) said transfer mechanism is operatively disposed between a flexing portion of the detector and said converting member to transmit changes in the form of the deflector to said axial force.
In a particularly preferred embodiment, the detector comprises a resilient disc shaped member mounted on said slider and having a scratch recording layer bonded to a front face of the member turned toward said front end of the pig bonded to a scratch recording layer. The scratch recording layer possesses resiliency sufficient for the layer to follow deformation of the resilient detector and return of the detector to a non-deformed state. Furthermore, the scratch recording layer it has smoothness and softness sufficient for the layer to become and remain scratched when the detector engages an anomaly of a predetermined minimum radial magnitude and when the detector returns to said non-deformed state. Thus, after passage of the pig through the pipeline, the front face of the disc indicates the nature and magnitude of anomaly or anomalies encountered during the passage by way of scratched portions of the recording layer.
In another aspect, the invention provides, for use in a pipeline caliper pig including a body provided with support and drive members for sliding engagement with the interior of the pipeline to drive the body coaxially through the pipeline by the flow of fluid in the pipeline:
an elastomeric, generally disc-shaped detector compatible with said body for securement thereto, said ring comprising;
(a) a first face, an axially opposed second face, and a circular circumferential edge portion having a predetermined diameter smaller than the inside diameter of the pipeline;
(b) said first face having a forward surface possessing:
(I) resiliency sufficient to follow resilient deformations of the ring and to return, with the ring, from a deformed to a non-deformed state;
(ii) smoothness and softness sufficient to become and remain scratched by obstacles in the pipeline as the detector,; secured to said body, advances through the pipeline.
Yet another embodiment of the present invention is generally characterized by a combination, wherein a detector, particularly for use in a caliper pig for detecting an obstruction in a pipeline, is provided. It comprises, in general terms, a resiliently deformable body including a securement portion adapted to be secured to a support, and a flexing portion spaced from the securement portion and adapted to flex relative to said support when subjected to a force in a predetermined direction;
said body comprising
a resiliently deformable first member having a leading face and a trailing face and
a resiliently deformable second member having a leading face and a trailing face;
the trailing face of said first member being turned toward the leading face of said second member; the distance between the trailing face of said first member and the leading face of said second member being at a predetermined minimum when the body is in a relaxed state;
signal generating means disposed in said flexing portion of the body and remote from said securement portion thereof,
said signal generating means comprising:
a first generating element secured to said first member; and
a second generating element secured to said second member in an alignment with the first generating element when the body is in a relaxed state;
said first and second generating elements being adapted to co-operate to emit a first signal when the elements are close to each other, and a second signal, distinct from said first signal, when the elements are remote from each other due to a difference between the degree of flexing between the first and second deformable members.